1. Field of the Invention
The present invention relates to an exposure apparatus, and a method of manufacturing a device.
2. Description of the Related Art
With an improvement in packing density of elements in devices such as a semiconductor device, an exposure apparatus used to manufacture a device is required to transfer a finer pattern to a precise position on a substrate at a precise size. To transfer a pattern onto the substrate at a precise size, it is necessary to improve the focus accuracy of matching the imaging plane (focal plane) of a projection optical system with the substrate surface. Also, to form a pattern image at a precise position on the substrate, it is of prime importance to maintain the projection magnification of the projection optical system at a target magnification.
The optical characteristics of a projection optical system, such as its imaging plane position (focus position) and projection magnification, can be adjusted to optimum states before an exposure apparatus is used. However, the optical characteristic of the projection optical system may change due to various factors. One of the factors which change the optical characteristic of the projection optical system is a change in temperature of the projection optical system due to heat from the exterior of the projection optical system. The temperature of the projection optical system may change due to factors other than those associated with exposure energy. The factors of a change in temperature of the projection optical system include, for example, a temperature control error of a thermostatic chamber in the exposure apparatus, and heat generated by a motor which drives a stage.
Japanese Patent Laid-Open No. 2005-203522 discloses a method of controlling the temperature of the outer surface of a barrel of a projection optical system to stabilize the temperature of the projection optical system. Japanese Patent Laid-Open No. 2003-59807 discloses a method of predicting a change in optical characteristic using a power polynomial model for the temperature measurement value at a specific position in an exposure apparatus, and correcting the change in optical characteristic.
As described above, to transfer a fine pattern onto the substrate, it is of prime importance to suppress a change in temperature of the exterior of the projection optical system, or to predict and appropriately correct the influence of a change in temperature of the exterior of the projection optical system. Heat generated in the exposure apparatus may be transferred to the projection optical system upon heat conduction, convection, or thermal radiation between members that constitute the exposure apparatus, and change the temperature of the projection optical system. Therefore, a change in temperature of a temperature measurement portion does not always immediately change the optical characteristic of the projection optical system, and a change in optical characteristic of the projection optical system generally appears with a predetermined time lag from the change in temperature. The methods of correcting the optical characteristic in the related art techniques often cannot correct the optical characteristic with a sufficient accuracy due to this time lag.